1. Field of the Invention
The present invention relates to a pitch stabilized, high-speed displacement vessel with which the pitching movement center of the hull is located in the midship area of the hull or forwardly of the midship area.
In conventional seagoing displacement vessels, the center of pitching motion of the hull has been located more towards the stern of the hull than towards the bows.
By pitching movement is meant the movement of the vessel or hull in its vertical midship plane as the vessel moves through the water. As the vessel moves through the water, it is also subjected to heaving movement, which can be considered as the vertical, parallel displacement to which the vessel is subjected as it follows the waves up and down.
Thus, the vertical acceleration forces that act on the vessel at a given point are determined partly by heave and partly by pitch, i.e. the angular acceleration of the vessel times the lengthwise distance between the center of pitching movement of the vessel and said given point.
Pitching movement, i.e. angular acceleration of the vessel, is, of course, dependent on the forward speed of the vessel in relation to the speed and direction of the waves, the relative speed between wave and vessel playing an important part in the acceleration of the vessel pitching movement.
Vertical movement of a seagoing vessel, and particularly vertical acceleration, is considered to be the greatest contributory factor to seasickness and it has been found generally that conventional catamarans whose center of pitching movement is located far out towards the stern and which are propelled at high speeds are extremely liable to subject passengers to powerful vertical acceleration forces. Naturally, it is also highly disadvantageous to subject the cargo of a vessel to pronounced vertical movements and to vertical acceleration forces in particular.
2. Description of related Art
In conventional displacement vessels, the height of the hull above the water and the pitching tendencies of the hull can be controlled with the aid of active stabilizing fins, which are controlled with the aid of sensors that detect the vertical acceleration of the vessel. Such control systems, however, are unsuitable for several reasons. For instance, the system must be capable of working very rapidly and includes movable fins which are sensitive to their own movement and which must be subjected to very powerful forces if they are to have any appreciable effect. Any malfunction of the fins or of the fin control system will place the vessel and the passengers at great risk and may have disastrous consequences should the malfunction occur at high speeds, for instance speeds of 35 knots, and in heavy seas.
The object of the present invention is to provide a seagoing vessel, preferably a multi-hull vessel, and more preferably a vessel of the catamaran type, in which the hull is a displacement hull and is constructed for propulsion at high speeds and in significant wave heights, for instance wave heights of 5 meters or higher. A vessel of this kind may have a length of 120 meters and width of 40 meters.
In accordance with one proposed construction of long, slim displacement hulls intended for high-speed seagoing vessels, for instance multi-hull vessels of the catamaran type, the forward part of the hull has a bulbous underwater body and a relatively narrow waterline-width, so that the forward part of the hull will have a hull shape similar to the hull shape of so-called SWATH-vessels, while the rearward part of the hull has a more rectangular cross-sectional shape. In this regard, the cross-sectional area of the hull located beneath the water line may vary along its length to a lesser extent than in the case of conventional high-speed seagoing vessels, and the cross-sectional shape of the hull may change generally continuously between the two aforesaid cross-sections.
The aforementioned hull configuration, developed by Applicants, is described in more detail in Patent Publication SE-A-9100288-1 (see U.S. Pat. No. 5,269,245) to which reference is now made for more detailed information relating to a hull configuration that can be taken as a suitable starting point for particularly favourable application of the present invention.
A hull which has the configuration taught by publication SE-A-9100288-1 obtains a center of pitching movement which is located relatively far forwards, namely in the midship region of the hull or forwardly thereof, for instance in a position corresponding to 75% of the length of the hull as measured from the stern of the hull, while the hull is well adapted for high forward speeds and can be advantageously fitted with water-jet units and is able to withstand heavy loads. Other advantages afforded by a hull of this configuration are disclosed in the aforesaid patent publication.
The invention is defined in the following claim 1 and further developments of the invention are defined in the subordinate claims.